This invention is directed to a mechanized lay up assembly line utilized for lay up and debulking of composite materials on lay up tools.
Because of high strength coupled with light weight, composite parts are being increasingly used as structural components in a variety of articles including air craft. Typical composite part materials include glass or graphite fibers that are embedded in resins such as epoxy, phenolic or bismaleimide resins. Generally the fiber and resin is "laid up" over a die or mold and then is cured under elevated temperature and pressure.
Composite parts destined to be used in air craft must meet exacting requirements as to their structural integrity. To meet these exacting requirements, precise control of lay up, debulking, and cure is required.
A widely utilized system for forming composite structural parts uses materials that are identified as "prepregs". These are sheets of fiber that have uncured resin embedded therein. The prepreg is positioned in a forming die or tool and is then subjected to heat and pressure to cure the prepreg into the composite material. A prepreg may be initially formed into a composite structure directly in the forming tool or it may be laid up on an additional tool identified as a lay up tool and then later transferred to the forming tool.
Certain patents are known that will assist the artisan in forming composite structures. These include U.S. Pat. No. 4,944,824 that generally reviews the physical steps that occur during prepreg cure. They further include U.S. Pat. No. 4,963,215 that discloses a method for debulking pre-cured thermal plastic composite laminae. Additionally, they include U.S. Pat. No. 4,869,770 that discloses a method of preventing buckling of thermal plastic composite laminates during cure; U.S. Pat. No. 4,900,379 that discloses a method of assisting lay up of layers of prepreg by printing patterns with an ink jet on the prepreg layers; and finally, U.S. Pat. No. 4,133,711 that discloses a mechanized apparatus for cutting, moving and stacking prepreg materials prior to lay up of these materials on a tool.
The tools utilized for prepreg lay up and cure must meet exacting standards as to dimensions and stability. This normally requires that these tools be of a sufficient size to maintain dimensional stability and be of a material having a low thermal expansion or a controlled thermal expansion. Typical of such tools are aluminum alloy metallic tools and bulk graphite tools. By their very nature such tools are heavy and are usually of such a size as to preclude direct manipulation of the tool by a human without some sort of mechanical assistance.
To form a composite part, various plies of prepreg are individually draped over or into the lay up tool by a technician. This lay up is facilitated by raising the temperature of the prepreg to soften it and make it more pliable. Such heating can be accomplished by the use of heat guns, infrared lamps, or by heating the tool itself. The plies are generally smoothed on one another to avoid wrinkles and to achieve the desirable ply orientation. Prior to subjecting the prepreg material to a heat and pressurization cure cycle, the plies are generally debulked or consolidated. Such debulking or consolidation insures that the plies assume the shape of the lay up tool and removes air bubbles or other voids between individual ply layers. It is often desirable to debulk and consolidate several times during the lay up of the plies, especially if a large number of plies are utilized for a composite part.
As heretofore practiced, a lay up tool would be moved by mechanical means, as for instance forklifts, gantries or other mechanical assisting devices to a position wherein a lay up technician could gain access to the tool. The technician then applies a number of plies of prepreg to the tool. If consolidation is required between application of plies a consolidation diaphragm needs to be applied over the tool and a vacuum introduced between the tool and the diaphragm. Once consolidation is complete, the lay up technician can then proceed to complete the lay up of additional plies. Lay up technicians are humans of different statures. Thus because the lay up technicians come in different sizes and temperaments, tooling positioning that is optimally placed for one technician may not be optimally placed for a further technician.